The present invention relates to a process for etching copper with an ammoniacal etchant solution and reconditioning the used etchant solution. According to the process of the present invention, only feeds of oxygen and water are consumed for etching copper and the amount of residual pollutant is significantly minimized.
The etching of copper is carried out for many purposes which include cleaning copper surfaces, providing a desired pattern on the copper surface and providing a conductive image on a copper clad laminate in the production of printed circuit boards.
With the rapid progress of electronic industry, there has been an increasing demand for high quality printed circuit boards in large amount. In the production of printed circuit boards with conductive images on electrically insulative substrates, the etching of cladded copper is critical to the quality of the printed circuit board. Many etchants for this purpose have been developed, of which the ammoniacal etchants are considered most representative. Ammoniacal etchants has high selectivity toward metals (they do not attack gold, nickel, lead or tin and thus are commonly used in the production of double-sided, multilayer or flexible printed circuit boards. To reduce the cost of production and the hazard of residual pollutants, many processes for reconditioning the used etchant solution have been developed. The reconditioning of the used etchant solution provides as least two advantages: (1) recovering valuable copper solute from the etchant, and (2) reducing the consumption of etchant solution. However, the presently known processes, some examples of which are cited below, are still far from being satisfactory and efforts have been taken to find improved process for reconditioning the used etchant solution.
U.S. Pat. No. 4,490,224 and UK Patent No. 2133806 A disclose similar processes in which the copper solute in the used etchant solution is recovered by electroplating the copper ion onto the cathode in an electroplating cell in which a semi-permeable membrane is interposed between the cathode and the anode to keep the copper ion to the side of the anode. These processes suffer from disadvantages including high electricity consumption, low production rate and high initial investment.
U.S. Pat. No. 4,083,758 discloses a process in which the copper solute in the etchant solution is recovered by extracting copper ion from the aqueous phase into an organic solvent phase, transporting the organic solvent phase into a reactor to react the copper ion with an acid (such as sulfuric acid) and then recovering copper by electrolysis. The process is most prominently implemented by Sigma Engineering AB of Sweden. The major disadvantages of the process are (1) the quality of the reconditioned etchant solution is adversely affected by the residual organic solvent in the reconditioned etchant solution, (2) high electricity is required, (3) the initial investments is high, and (4) large area for the installation of the apparatus is required.
U.S. Pat. No. 4,303,704 discloses a process to reduce the copper value in the used etchant solution by ion exchange resin. Ion exchange resin is generally used for extracting copper content in low concentration such as that in rinse water. The concentration of copper in such solution is measured by ppm. However, for used etchant solution in which the concentration of copper ion is generally as high as 100-180 grams per liter, the process is apparently impractical.
U.S. Pat. No. 4,280,887 discloses a process for reconditioning used etchant solution in which aluminium or aluminium ion is used to substitute copper ion in an electrochemical process to form precipitates of Al(OH).sub.3 and Cu. The precipitates are thereafter separated. The process requires the employment of metal aluminium to form the aluminium hydroxide precipitate and therefore has a great disadvantage in that the separation of the coprecipitated copper and aluminium hydroxide is very costly and may result in severe pollution problem.
In view of the above, there has not been any process which can satisfactorily, effectively and economically recondition the used etchant solution of copper.